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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2008/
Module Title: Thermofluids
Module Code: BULD 6009
School: Mechanical & Process Engineering
Programme Title: Bachelor of Engineering in Mechanical Engineering Bachelor of Engineering in Building Services Engineering
Programme Code: EMECH_7_Y2, EBSEN_7_Y
External Examiner(s): Mr. Alan Bateman and Dr. Patrick Delassus Internal Examiner(s): Ms. M. Kavanagh
Instructions: Answer any 3 questions. Please tick off which questions you attempt on the front of the script.
Duration: 2 hours
Sitting: Summer 2009
Requirements for this examination: Steam Tables, Log Tables
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you are attempting the correct examination. If in doubt please contact an Invigilator.
Q1 Internal Combustion Engine
(a) Sketch a typical indicator diagram for a four-stroke cycle petrol engine, and explain each process of the cycle. (5marks)
(b) Discuss the two enclosed areas of the indicator diagram in relation to the work done by the engine. (3marks)
(c) Identify, clearly, on the indicator diagram a heat transfer process. (2 marks)
(d) A four cylinder, four-stroke cycle petrol engine has a bore 90mm and a piston stroke 90mm. Running at 80revs/s, the indicated mean effective pressure is 630kN/m^2 and the fuel consumption in an hour is 12kg. The mechanical efficiency is 80%. The calorific value of the fuel is 43MJ/kg. Determine: (i) The indicated power. (9 marks) (ii) The brake power. (4 marks) (iii) The indicated thermal efficiency. (5 marks) (iv) The brake thermal efficiency. (5 marks)
Q2 Expansion and Compression of gases
(a) A cycle consists of the following processes in order: (1) adiabatic compression (2) constant volume heating (3) adiabatic expansion (4) constant volume cooling Sketch the cycle on a P-V diagram and on it clearly identify each process. (6 marks)
(b) State what is meant by an adiabatic process and give a practical example of such a process. (4 marks)
(c) 1kg of air is compressed adiabatically from an initial volume of 1.04m^3 to a final volume of 0.173m^3. At the start of the compression, the pressure and temperature are 103kN/m^2 and 100 o^ C respectively. For air take R= 287J/kg K, γ = 1.4. (i) Determine the pressure and temperature of the compressed air. (8 marks) (ii) Determine the work done. (13 marks) (iii) Is the work done on the gas or by the gas? (2 marks)
